Nonwoven fabric and method of making the same



March 17, 1970 A, H. DRELlcH ETAL 3,501,369

NONWOVEN FABRIC AND METHOD OF MAKING THE SAME Filed Nov. 17, 1965 TTORNE Y i INVENTORS I States Patent 3,501,369 Patented Mar. 17, 1970 Int. Cl. D04h 1/04 vU.S. Cl. 161-150 12 Claims ABSTRACT OF THE DISCLOSURE A new nonwoven fabric having improved wet strength and comprising from 25 to `95 percent of cellulosic fibers and 5 to 75 percent of polypropylene fibers. The polypropylene fibers are partially fused but maintain their fibrous identity and are uniformly distributed throughout the cellulose fibers in bonding relationship. The fabric is made by forming a web of the combination of fibers and heating the web to a temperature of from about 325 F. to 400 F. and applying from about 2 to .20 pounds per linear inch of pressure to the web to partially fuse the polypropylene fibers and bond the polypropylene fibers and cellulose fibers together.

The present application is a continuation-in-part application of our copending application Ser. No. 416,041 filed Dec. 4, 1964 now abandoned.

This invention relates to nonwoven fabrics of cellulose fibers and to methods of making the same. More particularly the invention relates to nonwoven fabrics of cellulose fibers bonded with a polypropylene resin distributed throughout the fibers and in bonding relationship therewith and to methods of making such nonwoven fabrics.

In all known nonwoven fabrics, the strength of the fabric decreases when the fabric is wetted, i.e., the wet strength of known nonwoven fabrics is generally less and in most instances substantially less than the dry strength of the fabric.

We have discovered a new nonwoven fabric which unexpectedly has improved wet strength as compared to the dry strength of the fabric, i.e., the strength of our fabric unexpectedly increases when the fabric is wetted.

Our new nonwoven fabric comprises a web of cellulose fibers, preferably cotton fibers, bonded in an obvious intermittent configuration of binder areas, said binder being fused polypropylene fibers. The new nonwoven fabric of the present invention contains from about 5% to 75% based on the weight of the fabric of polypropylene fibers, or in certain instances as will be explained hereinafter, an even higher percentage of polypropylene fibers with the remainder of the fabric being cellulose fibers, that is, generally from about 25% to 95% by Weight of the fabric. The polypropylene fibers must be uniformly distributed throughout the cellulose fiber web in an intermittent manner either randomly or in a pattern. In all instances there are substantial portions of the web between bnder areas which contain substantially only ce1- lulose fibers.

The fabric of the present invention is bulky and lofty, is moderately strong and has higher wet strength than dry strength and in all instances considerably more strength than the unbonded fabric.

The fabrics of the present invention are suitable for use as wiping cloths, especially in those areas where it is desired to wipe water or aqueous solutions because of the excellent wet strength of the fabric coupled with its good absorbency characteristics. The fabric is also suitable for surgical purposes due to its softness, loft and absorbency.

The fabric of the present invention is produced by forming a web of cellulose fibers and distributing in this Web from about 5% to 75% or more based on the weight of the final fabric of polypropylene fibers. The polypropylene fibers are distributed in an obvious intermittent configuration of binder areas, and the web with the polypropylene fibers therein heated to soften the polypropylene and pressure applied to bond the web of cellulose fibers.

The maximum amount of polypropylene fibers used in the fabric Will depend for the most part on the amount of fusion or bonding used in producing the bonded fabric. If high temperatures, pressures and long times are used in the bonding of the fibers so that all of the polypropylene fibers are fused, the percentage of polypropylene fibers in the web should be kept at the lower end of the range; however, if a light fusion takes place so that only a portion of the polypropylene fibers are fused, the percentage of polypropylene fibers inthe web may be 50% to 75 by weight or even more if desired.

The invention will be more fully understood from the description which follows, taken in conjunction with the accompanying drawings in which a novel fabric of the present invention is depicted along with a flow sheet showing the steps for producing the present invention. In the drawings:

FIGURE 1 is a plan View of a nonwoven structure of the present invention, and

FIGURE 2 is a fiow sheet diagrammatically showing the type of operations by which the present invention may be carried into practice.

Referring to the drawings, in FIGURE l there is shown a web 10 of cotton fibers 11 having randomly distributed throughout the web fused polypropylene fibers 12. The polypropylene fibers have been activated with heat and pressure to bond the cellulose fibers together.

The starting materials from which the fabrics of the present invention are produced are webs of cellulose fibers. The Webs may have an orientation, that is, have a majority of the fibers aligned in either the long or cross direction of the web, or they may be iso-oriented, that is, have no predominate fiber direction. The web may comprise natural fibers, such as cotton fibers or artificial fibers, such as rayon fibers. In many instances the web may concabin the bonding material to be used, that is, polypropylene ers.

If cotton fibers are used, they may be gray or bleached, fine or coarse, mature or immature. Generally the length of the cotton fibers will be from about 2 inches down to V8 inch or less.

The rayon fibers used generally have a length of from about 1/4 inch to 2 inches or longer and have a denier from about 1 to 5 or even higher.

The polypropylene bonding material is in the form of fibers which preferably are distributed throughout the web of cellulose fibers when the web is formed though they may be distributed after the web is formed.

The polypropylene fibers may vary in length from 1/2 inch or lower up to l/ or 2 inches and even longer. Generally the denier of the polypropylene fibers will be in the range of from about 1 to 5 though higher denier fibers may be used.

In all instances the cellulose fiber web is bonded in an intermittent configuration of Ibondin-g areas leaving considerable portions of the web unbonded. The polypropylene bonding material covers no more than about 20% of the total surface of the web, and is preferable that the polypropylene bonding material cover considerably less surface, that is, from about 10% down to about 2% of the total surface of the web. Though only 20% of the total surface contains polypropylene bonding material, there may be considerably more polypropylene fibers present. If high percentages of polypropylene fibers are used, the bonding conditions used may be less stringent so that only a portion of the polypropylene fibers bond to each other leaving a portion of substantially unbonded polypropylene fibers in the final product.

The amount of polypropylene fiber used may vary from about to 75% or even higher of the total weight of the final nonwoven fabric and preferably from about 5% to 25% of the total weight of the fabric. If less than 5% by weight ofvpolypropylene fiber is used, the resultant fabric has little strength, and in most instances substantially no more strength than the original fabric. If more than 75 polypropylene liber is used and also dependent on the degree of bonding attained, the fabric loses the characteristic properties of the cellulose fiber, such as, absorbency, softness and loft, and also the cost of the fabric is greatly increased, as generally the polypropylene fiber is more expensive than the cellulose fibers,lespecially short cotton fibers.

Referring to the iiow diagram, FIGURE 2, the starting material may 4be either a web of 100% cellulose fibers (Box 1) or a web of cellulose fibers containing polypropylene fibers (Box 2). If the former is used, the polypropylene fibers are applied after the cellulose fiber web is formed (Box 3). In both instances the polypropylene fibers are activated to bond fibers together by the application of heat to soften the polypropylene fibers and the application of pressure to bond cellulose and polypropylene fibers together. Heat and pressure may be applied simultaneously (lBox 4) or separately (Box 5 and Box 6) provided the pressure is applied while the polypropylene fibers are in the softened state. In both instances the improved wet strength nonwoven fabric (Box 7) of the present invention is produced.

In carrying our invention into practice, the starting web of cellulose and polypropylene fibers, may be produced by any of the techniques well known in the art, for example, carding operations, air-laying operations, waterlaying operations, and the like. In those instances where the polypropylene fiber is to be applied after the web is formed, any of the various techniques may be used, for example, sprinkling polypropylene fibers on or between light-Weight webs either in a random or predetermined pattern.

The polypropylene fibers are softened by heating the web with the polypropylene therein to temperatures of from about 325 F. to 400 F. for periods of time from about 3 to 4 seconds (if using infrared radiation), Or almost instantaneously (if calendered) to one minute or longer (if an oven is used).

While the polypropylene -iibers are in the softened state,

light pressure is applied to the web. The pressure may be applied simultaneously with the heating of the polypropylene fibers, e.g., by a pair of heated calendar rolls or pressure may be applied after the polypropylene fibers have been heated provided they are still in the softened a state, e.g., by passing the web through an oven and then calendering themheated web with a pair of cool rolls. IPressures of from about 2 to 20 pounds per linear inch have been found suitable when using calendering rolls to apply pressure to webs which have been heated to a temperature of about 340 F. However, other pressures may also be used depending on the melt index of the polypropylene fiber, the temperature to which the web is heated and the lengths of time both heat and pressure are applied to the web.

It is believed that the polypropylene fibers must be only partially fused, if insufiiciently fused, the cellulose fibers are not bonded and if completely fused, the polypropylene fibers become spheres, lose their fibrous shape, and do not improve fiber wet strength, It is also believed that maintaining the fiber shape of the polypropylene in the final fabric produces a wrap-around bond of the cellulose fibers as contrasted to the embedding of the cellulose fibers in polypropylene and this wrap-around bonding may Ibe what increases the wet strength of the nal nonwoven fabric. The term fiber shape as used herein means that the length of the polypropylene material is appreciably greater than the width of the polypropylene material, i.e., that the polypropylene material is at least three times as long as it is wide. The higher the percentage of polypropylene fibers used in the web, the less stringent the bonding conditions necessary to attain the advantages of the invention.

If desired, the fabrics of the present invention may be after treated with softeners, dimensional stabilization agents, mercerizing solutions or any of the various other treatments known in the art.

In order to more clearly disclose the invention, several specific examples will now be described.

Example I A plurality of Iwebs are formed on carding machines. The total weight of the Webs formed is 900 grains per square yard, and the web contains bleached comber cotton having an average length of approximately 1/2 inch and 3 denier per filament polypropylene fibers having a length of 11/2 inches. The web is heated to approximately 325 F. by passing it through a calender which applies approximately 20 pounds per linear inch gauge pressure to the web. The calender consists of a pair of heated rotating rolls. The |wet strength and the dry strength of this web are then determined by an Instron tester in accordance ywith Nonwoven Fabric Standard Testing Methods ASTM D-lll7-63. In testing the wet strength of the fabric, the piece to be tested is immersed in water and placed on kraft paper for ten seconds to remove the excess water before testing. The dry strength of this fabric in a machine direction, that is, the direction which the fabric is produced is 141 grams per inch of width while the wet strength of this fabric is 468 grams per inch of width. The dry strength in the cross direction of the fabric is 31.8 grams per inch of width while the wet strength is 90.7 grams per inch of width.

Example II A fibrous web weighing 1050 grains per square yard is produced by a group of carding machines. The web contains 80% 11/2 inch 3 denier rayon fibers and 20% 11/2 denier 11/2 inch polypropylene fibers. The polypropylene fibers are activated by passing the web through a bank of infrared heaters set at a wave length radiation range from about 2.8 microns to 3.2 microns. The heated web passes through the nip formed by a pair of chilled rolls cooled to about 50 F. separated by approximately .005 inch to .010 inch. The web is calendered and cooled by these rolls. The dry and wet tensile strengths of this fabric are determined as in Example I. The dry strength of this fabric in the machine direction is 509 gra-ms per inch of width while the wet strength increases to 845 grams per inch of width. The dry strength of this' fabric in the cross direction is 136 grams per inch of 'width while the wet strength of this fabric increases to 218 grams per inch of width.

Example III A cotton web weighing about 450 grains per square yard is produced. Approximately 450 grains of a polypropylene powder is uniformly distributed throughout the web. The web is then calendered at 320 F. with a pressure of approximately 2 pounds per linear inch to bond the fibers together. The resultant fabric is tested for dry and wet tensile strengths as in kExample I. The dry strength in the machine direction is 422 grams per inch of width while the wet strength is 345 grams per inch of width whereas the dry strength in the cross direction is 100 grams per inch of width and the wet strength remains at 100 grams per inch of width. There is no improvement in the `wet strength of the fabric.

Example 1V The procedures of Example I are carried out as set forth therein with the exception that the concentration of cotton fibers is raised from 90% to 95 in the present example, and the concentration of polypropylene fiber is reduced from to 5% in the present example. Comparable results to the results of Example I are obtained.

Example V A 950 grain weight card web is produced. The web contains 90% cotton fibers and 10% Vinyon fibers. The Vinyon fibers are 3 denier approximately 11/2 inches long. The web is heated to approximately 230 F. at a pressure of pounds per linear inch by a calender. The web is then tested for dry and wet strength as previously described. The dry strength in the long direction is 313 grams per inch of lwidth and the wet strength decreases to 284 grams per inch of width. The dry strength in the cross direction is 147 grains per inch of width and the wet strength decreases to 84 grams per inch of width.

Example VI A 100% cotton web weighing approximately 600 grains per square yard is print bonded in a horizontal wavy line pattern (4 lines per inch) with a hydroxyethylcellulose bonding material. The amount of add-on of hydroxyethylcellulose in the final fabric is approximately 3% based on the weight of the fabric. Tested as described in Example I, the dry strength of this fabric in the long direction is 762 grams per inch of width While the wet strength is 731 grams per inch of width. The dry strength in the cross direction of this fabric is 236 grams per inch of `width and the wet strength drops sharply to 77 grams per inch of width.

Example VII For comparative purposes and to show that the abovedescribed examples do have increased strength over an unbonded web the dry and wet tensile strength of an unbonded 4100% cotton web are tested as described in Example I. The dry strength of such a web in the long direction is 43 grams per inch of width while the wet strength is 154 grams per inch of width. The dry strength in the cross direction is 8 grams per inch of width while the wet strength in the cross direction is 58 grams per inch of Iwidth.

Example VIII A fibrous web weighing 200 grains per square yard is produced by a group of carding machines. The web coritains 50% 2-inch, 11/2 denier rayon fibers and 50%, 11/2 inch, 11/2 denier polypropylene fibers. The web is bonded with a hand iron at 300 F. using normal hand pressure. The dry and wet tensile strengths of this fabric are determined as in Example I. The dry strength of this fabric in the machine direction is 644 grams per inch of 'width while the wet strength of this fabric is 692 grams per inch of width. The dry strength in the cross direction of the fabric is 81.6 grams per inch of width while the Wet strength is 86.2 grams per inch of width.

It should be clearly understood, however, that the above examples are for the purposes of illustration only, and are not to be used to delineate the breadth or scope of the invention. The invention is only limited by the scope of the claims appended hereto.

What is claimed is:

1. A nonwoven fabric having improved wet strength comprising: from about to 95% by weight of the fabric of cellulose fibers and from about 5% to 75% by weight of the fabric of partially fused polypropylene fibers said partially fused polypropylene fibers being in a fibrous shape in the fabric and being uniformly distributed throughout the cellulose fibers and in bonding relationship therewith, said fabric having substantial areas free of partially fused polypropylene fibers.

2. A non-woven fabric having improved wet strength comprising: from about to 95% by weight of the fabric of cellulose fibers and from about 5% to 25 by weight of the fabric of partially fused polypropylene fibers, said partially fused polypropylene fibers 4being in a fibrous shape in the fabric and being uniformly distributed throughout the cellulose fibers and in bonding relationship therewith, said fabric having substantial areas free of partially fused polypropylene fibers.

3. The fabric of claim 1 in which the polypropylene fibers are disposed in an obvious intermittent pattern.

4. The fabric of claim 2 in which the polypropylene fibers are disposed in an obvious intermittent pattern.

5. The fabric of claim 1 in which the partially fused polypropylene fibers cover from about 2% to 20% of the total surface of the fabric.

6. The fabric of claim 2 in which the partially fused polypropylene fibers cover from about 2% to 20% of the total surface of the fabric.

'7. A nonwoven fabric having improved wet strength comprising: from about 75% to 95% by weight of the fabric of cellulose fibers and from about 5% to 25 by weight of the fabric of partially fused polypropylene fibers, said partially fused polypropylene fibers being in a fibrous shape in the fabric and individual polypropylene fibers -being wrapped around a plurality of cellulose fibers.

8. The fabric of claim 7 in which the cellulose fibers are cotton fibers.

9. The fabric of claim 7 in which the cellulose fibers are rayon fibers.

10. A method for producing a nonwoven fabric having improved wet strength comprising: forming a web of cellulose fibers having distributed throughout said web from about 5% to 75 based on the weight of the final fabric of polypropylene fibers, heating the web to a temperature of from about 325 to 400 F. to soften the polypropylene fibers and applying from about 2 pounds per linear inch to 20 pounds per linear inch of pressure to said web while the polypropylene fibers are in the softened state whereby said polypropylene fibers retain their fibrous shape and wrap around cellulose fibers to bond them together.

11. A method according to claim 10, wherein from about 5 to 25 percent based on the weight ofthe final fabric of polypropylene fibers are distributed throughout the cellulose fibers.

12. A method according to claim 10, wherein heat and pressure are applied to the web simultaneously.

References Cited UNITED STATES PATENTS 2,500,282 3/1950 Francis 161-150 2,647,297 8/ 1953 Battista 161--150 3,049,466 8/1962 Erlich 161-150 3,286,007 1l/1966 Wilkie et al. 264--119 3,287,474 11/1966` Harrington 264-122 MORRIS SUSSMAN, Primary Examiner U.S. C1. X.R. 161-170; 264-126 

